Field of the Invention
The present invention relates generally to lighting products and more particularly to optical lens devices, lighting systems, and associated methods for asymmetrically distributing light into an environment.
Description of the Related Art
Lighting systems based on light-emitting diodes (LEDs) are replacing conventional incandescent lights and fluorescent lights in many locations. Recently, linear lighting fixtures based on a plurality of lineally aligned LEDs are starting to replace fluorescent tubes for overhead fixtures. Unlike fluorescent tubes, which generally emit light uniformly about a cylinder, the LEDs of a linear lighting fixture are generally directional light sources that produce light over a relatively narrow range of angles rather than over a broad area. Thus, LED-based fixtures include additional components to redirect and diffuse the light to provide more uniform lighting. The additional components tend to be large and add considerable size and weight to what would otherwise be a small light fixture.
Conventional lighting products for illuminating environments typically include a light emitter such as a bulb or light emitting diode (LED) and a lens. Light emitted by the emitter is distributed in a desired pattern into the environment by the lens. In many applications, it is generally desirable to emit light in an asymmetric profile such that more light is distributed by the lens into a desired direction, and less light is distributed into non-preferred directions. Such applications for asymmetric lighting include street lighting where it is desirable to maximize the amount of light projected toward the street, but to minimize the amount of light projected away from the street toward nearby houses or buildings. Numerous other applications where asymmetric lighting profiles are desired from emitter and lens combinations are generally known in the art for both indoor and outdoor applications.
Asymmetric light distribution may be achieved in a variety of ways. For example, conventional devices for projecting light in a given direction include mechanical reflectors or shields that intercept light rays and redirect those light rays in a desired direction. Reflectors often have a polished surface to improve surface reflectivity to more efficiently reflect incident light. However, reflectors are often inadequate for many asymmetric lighting applications because they absorb photons and reduce lighting efficiency. Additionally, reflectors may become hot during use or may become damaged or misaligned, resulting in uneven light distribution profiles. Reflectors also may be expensive to produce and align in a mass production environment.
Others have attempted to overcome the problems of efficiently distributing emitted light in an asymmetric profile by providing a shaped lens over an emitter. The shaped lens may include a transparent or semi-transparent material having one or more exterior refractive surfaces. Emitted light travels through the lens material and is redirected in a desired direction upon contact with the exterior refractive surface.
One problem with conventional asymmetric lens devices is the use of primarily refractive exterior surfaces for distributing light asymmetrically. The use of refractive surfaces for the majority of light control often requires additional mechanical shields or reflectors to block light inadvertently distributed toward the desired dark region, or house side, of a lighting system. As such, conventional systems may require two components—a primarily refractive lens and a mechanical shield or reflector—for achieving satisfactory asymmetric light distribution. Additionally, conventional asymmetric lens devices do not achieve optimal efficiency and do not minimize unwanted light emission toward the desired dark regions.